The present application claims priority to Japanese Application No. P10-288984 filed Oct. 12, 1998 which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof and more specifically to a semiconductor device and a manufacturing method thereof which causes less characteristic fluctuation of elements and hardly causes a parasitic action even when the semiconductor device comprises a barrier metal made of a titanium material on an inter-layer insulating film.
2. Description of Related Art
FIG. 1 is a section view showing one structural example of a semiconductor device.
The semiconductor device shown in the figure is a so-called BiCMOS comprising a bipolar transistor 101, an N-channel type MOS (Metal Oxide Semiconductor) transistor 102, a P-channel type MOS transistor (not shown) and a MIS (Metal Insulator Semiconductor) type capacitor element 103 formed on the surface side of one and same semiconductor substrate 104. The bipolar transistor 101 is an NPN type bipolar transistor having a double poly-silicon structure suited for high speed and the MOS transistor 102 has a single drain structure. The capacitor element 103 is formed by using a silicon nitride film as a dielectric film 105.
An inter-layer insulating film 107 covering a gate electrode 106 of the MOS transistor 102 is composed of a first silicon oxide film 107a and a second silicon oxide film 107b. The first silicon oxide film 107a is a film for use as an opening of an active region of the bipolar transistor 101 and the second silicon oxide film 107b is a film formed on the first silicon oxide film 107a while covering a base electrode 109 of the bipolar transistor 101 and an upper electrode 110 of the capacitor element 103. Wires 108 are provided on the inter-layer insulating film 107 constructed as described above. Its electro-migration resistance and heat resistance are assured by constructing it by laminating, in order from the bottom, a titanium film, titanium nitride oxide film, a titanium film and silicon aluminum film.
However, the semiconductor device constructed as described above has had the following problems.
In the semiconductor device constructed as explained by using FIG. 1, the wire 108 is provided on the gate electrode 106 via the inter-layer insulating film 107 composed of the first silicon oxide film 107a and the second silicon oxide film 107b. Therefore, hydrogen which has been captured by dangling bonds at the interface between the silicon/silicon oxide film (i.e., the interface between the semiconductor substrate 104 and the gate oxide film 111) under the gate electrode 106 diffuse within the inter-layer insulating film 108 and are absorbed by the titanium film composing the wire 108 when a heating process such as a sintering process or an alloy processing for forming a titanium-gold alloy film on the back of the semiconductor substrate 104 is implemented after forming the wire 108. As a result, the dangling bonds increase at the above-mentioned interface, thus fluctuating the threshold voltage of the MOS transistor 102. Further, moisture within the thick silicon oxide film composing the inter-layer insulating film 107 diffuses under the gate electrode 106, thus deteriorating the hot-carrier resistance of the MOS transistor 102.
Meanwhile, as the BiCMOS type semiconductor device, there is also one using an inter-layer insulating film formed by laminating a silicon oxide film on a silicon nitride film as disclosed in Japanese Patent Laid-Open No. 2-32561.
In the semiconductor device disclosed in Japanese Patent Laid-Open No. 2-32561, the upper part of a MOS transistor is covered by a silicon nitride film for preventing the diffusion of hydrogen. Therefore, it is possible to prevent the hydrogen at the above-mentioned interface between the silicon/silicon oxide film under the gate electrode 106 from diffusing by the silicon nitride film even when the above-mentioned heating process is carried out after forming the wires above the silicon nitride film. Accordingly, it enables the prevention of the dangling bonds from increasing at the abovementioned interface. Still more, because the silicon nitride film also shuts down the diffusion of moisture, it is possible to prevent the moisture within the silicon oxide film composing the inter-layer insulating film from diffusing under the gate electrode. Accordingly, it allows the hot-carrier resistance of the MOS transistor to be assured.
However, because the upper part of the bipolar transistor is also covered by the silicon nitride film in this semiconductor device, a number of dangling bonds is kept small at the interface between the silicon and the silicon oxide film in the bipolar transistor (e.g., at the interface between the semiconductor substrate and the field oxide film in the above-mentioned publication). Accordingly, the current amplification factor (hFE) of a parasitic PNP bipolar transistor composed of a base/collector/substrate in the NPN type bipolar transistor becomes high.
Further, because an element isolating region for isolating the MOS transistors is also covered by the silicon nitride film in the semiconductor device described in the above-mentioned publication, hydrogen at the interface between the field oxide film and the semiconductor substrate composing the element isolating region are assured, thus preventing the dangling bonds from increasing. Therefore, threshold voltage (Para-Vth) of the parasitic MOS transistor formed between the adjoining MOS transistors becomes small. As a result, it has had a problem that a parasitic action is liable to occur.
Accordingly, it is an object of the present invention to provide a semiconductor device, and a manufacturing method thereof, which causes less characteristic fluctuation of elements and hardly causes parasitic action even if it comprises a barrier metal composed of a titanium material on an inter-layer insulating film.
In order to achieve the above-mentioned object, an inventive semiconductor device comprises a MOS transistor provided on the surface side of a semiconductor substrate; a silicon oxide insulating film and a silicon nitride insulating film provided on the semiconductor substrate while covering the MOS transistor; and wires having a barrier metal made of a titanium material and provided above these insulating films and is characterized in that the silicon nitride insulating film covers the MOS transistor and has an opening on an element isolating region for isolating the MOS transistors.
Because the silicon nitride insulating film covering the MOS transistor becomes a barrier in the semiconductor device constructed as described above, hydrogen which has been captured by dangling bonds at the interface between the semiconductor substrate and a gate oxide film will not reach to the wires provided above the silicon nitride insulating film. Therefore, it is possible to prevent the hydrogen from being absorbed by the barrier metal made of the titanium material constituting the wire and to suppress a number of dangling bonds from increasing at the above-mentioned interface. Accordingly, the threshold voltage of the MOS transistor is stabilized.
Further, because the silicon nitride insulating film becomes the barrier, it prevents moisture above the silicon nitride insulating film from diffusing down to a gate electrode of the MOS transistor. Therefore, the hot-carrier resistance of the MOS transistor may be assured.
Still more, because the opening of the silicon nitride insulating film is provided on the element isolating region for isolating the MOS transistors, hydrogen at the interface between the silicon oxide film and the semiconductor substrate diffuses upward via the silicon oxide film when the silicon oxide film is provided in the element isolating region, thus increasing the dangling bonds at the interface. Therefore, threshold voltage (Para-Vth) of a parasitic MOS transistor formed between the adjoining MOS transistors become large. As a result, the parasitic actions of the MOS transistor hardly occurs.
When the bipolar transistor is provided on the surface side of the semiconductor substrate in the semiconductor device described above, the silicon nitride insulating film has an opening on the bipolar transistor.
Thereby, hydrogen at the interface between the semiconductor substrate and the silicon oxide insulating film in the bipolar transistor diffuses upward via the silicon oxide insulating film. Therefore, the dangling bonds increase at the interface, thus lowering a current amplification factor (hFE) of the parasitic bipolar transistor composed of a base/collector/substrate in the above-mentioned bipolar transistor.
A capacitor element comprising a dielectric film formed in the same process with that of the silicon nitride insulating film may be provided on the surface side of the semiconductor substrate in the semiconductor device. It allows the semiconductor device comprising the silicon nitride insulating film, the MOS transistor and the capacitor element to be obtained without increasing manufacturing steps.
An inventive semiconductor device manufacturing method comprises steps of forming a MOS transistor on the surface side of a semiconductor substrate; forming a silicon nitride insulating film covering the MOS transistor and having an opening on an element isolating region for isolating the MOS transistors above the semiconductor substrate; and forming a capacitor element on the surface side of the semiconductor substrate and is characterized in that it further comprises a step of forming the silicon nitride insulating film and the dielectric film of the capacitor element in the same time. In this step, an opening is created through the silicon nitride insulating film on the bipolar transistor provided on the surface side of the semiconductor substrate.
The above-mentioned semiconductor device manufacturing method allows the semiconductor device comprising the silicon nitride insulating film covering the MOS transistor together with the respective elements and having the opening on the element isolating region to be obtained with the same number of manufacturing steps with that for forming the semiconductor device comprising the MOS transistors, the capacitor element and (the bipolar transistors).
The specific nature of the invention, as well as other objects, uses and advantages thereof, will clearly appear from the following description and from the accompanying drawings in which like numerals refer to like parts.